Microkeratome blade

ABSTRACT

A microkeratome blade for use for the removal of the epithelial layer and underlying Basement Membrane while leaving a smooth and undisturbed Bowman&#39;s Membrane in preparation for a laser refractive surgical procedure. The blade is capable of cutting through the epithelial layer and Basement Membrane, but not capable of cutting through Bowman&#39;s Membrane.

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to the field of refractivesurgery and, more particularly, to microkeratomes used for performinglaser refractive surgery.

[0002] The human eye in its simplest terms functions to provide visionby transmitting light through a clear outer portion called the cornea,and focusing the image by way of a crystalline lens onto a retina. Thequality of the focused image depends on many factors including the sizeand shape of the eye, and the transparency of the cornea and the lens.

[0003] The optical power of the eye is determined by the optical powerof the cornea and the crystalline lens. In the normal, healthy eye,sharp images are formed on the retina (emmetropia). In many eyes, imagesare either formed in front of the retina because the eye is abnormallylong (axial myopia), or formed in back of the retina because the eye isabnormally short (axial hyperopia). The cornea also may be asymmetric ortoric, resulting in an uncompensated cylindrical refractive errorreferred to as corneal astigmatism. In addition, due to age-relatedreduction in lens accommodation, the eye may become presbyopic resultingin the need for a bifocal or multifocal correction device.

[0004] In the past, axial myopia, axial hyperopia and cornealastigmatism generally have been corrected by spectacles or contactlenses, but there are several refractive surgical procedures that havebeen investigated and used since 1949. Jose Barraquer, M. D.investigated a procedure called keratomileusis that reshaped the corneausing a microkeratome and a cryolathe. This procedure was never widelyaccepted by surgeons. Another procedure that has gained widespreadacceptance is radial and/or transverse incisional keratotomy (RK or AK,respectively). In the 1990s, the use of photablative lasers to reshapethe surface of the cornea (photorefractive keratectomy or PRK) or formid-stromal photoablation (Laser-Assisted In Situ Keratomileusis orLASIK) have been approved by regulatory authorities in the U.S. andother countries. Recently, a new version of PRK called Laser EpithelialKeratomileusis (LASEK) has been developed wherein the epithelial layeris soaked in alcohol so as to release it from Bowman's Membrane and theepithelial layer is non-destructively rolled aside and the underlyingstromal tissue is ablated in a manner similar to PRK. This proceduredoes not always allow for the smooth removal of the epithelial layer ina single sheet. In addition, alcohol is toxic to corneal tissue.

[0005] Accordingly, a need continues to exist for a device and methodfor the safe, consistent removal of the epithelial layer and BasementMembrane during the a laser refractive surgical procedure.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention improves upon the prior art by providing amicrokeratome blade for use for the removal of the epithelial layer andunderlying Basement Membrane while leaving a smooth and undisturbedBowman's Membrane in preparation for a laser refractive surgicalprocedure. The blade is capable of cutting through the epithelial layerand Basement Membrane, but not capable of cutting through Bowman'sMembrane.

[0007] Accordingly, one objective of the present invention is to providea safe and nontoxic method for the removal of the epithelial layer andunderlying Basement Membrane in preparation for a laser refractivesurgical procedure.

[0008] Another objective of the present invention is to provide a methodfor the removal of the epithelial layer in preparation for a laserrefractive surgical procedure without the use of toxic chemicals.

[0009] Another objective of the present invention is to provide a devicethat provides the safe and non-toxic method for the removal of theepithelial layer and underlying Basement Membrane in preparation for alaser refractive surgical procedure.

[0010] Another objective of the present invention is to provide amicrokeratome blade that provides the safe and non-toxic method for theremoval of the epithelial layer and underlying Basement Membrane inpreparation for a laser refractive surgical procedure.

[0011] These and other advantages and objectives of the presentinvention will become apparent from the detailed description and claimsthat follow.

BRIEF DESCRIPTION OF THE DRAWING

[0012]FIG. 1 is a schematic representation of a microkeratome that maybe used with the invention of the present method.

[0013]FIG. 2 is an enlarged partial side view of a microkeratome bladethat may be used with the method of the present invention.

[0014]FIG. 3 is a partial cross-sectional view of a human cornea.

DETAILED DESCRIPTION OF THE INVENTION

[0015] As best seen in FIG. 1, one microkeratome 34 that may be usedwith the method of the present invention generally includes suction ring10 sized and shaped so as to affixed to eye 12. Ring 10 includes guides14/16 opposite eye 12 that guide cutting head 40 across ring 10. Ring 10is connected through translation member 26 to stepper motor 28 forproviding linear movement of cutting head 40 across ring 10. Cuttinghead 40 contains blade 38 that is eccentrically connected to motor 36contained within housing 42 of microkeratome 34. Microkeratome 34 iswell-known in the art (see for example U.S. Pat. No. 6,071,293(Krumeich), the entire contents of which being incorporated herein byreference), and commercially available from sources such as AlconLaboratories, Inc., Fort Worth, Tex.

[0016] As best seen in FIG. 2, blade 38 that may be used with the methodof the present invention generally includes relatively flat side 100,tapered side 110 containing rounded section 112 and blunt tip 114connecting flat side 100 and rounded section 112. Rounded section 112generally has a radius of between about 0.025 millimeters and 0.200millimeters and is rounded through of angle δ of between approximately 5degrees and 60 degrees. Blunt tip 114 generally has a length L ofbetween approximately 0.001 millimeters and 0.050 millimeters, withbetween about 0.005 millimeters and 0.025 millimeters being preferred,and is ground at an offset angle Θ relative to rounded portion 112 atbetween approximately between 0 degrees and 60 degrees, with betweenapproximately between 0 degrees and 20 degrees being preferred Blade 38may be made of any suitable material, such as 400 Series stainless steeland may be made using conventional surgical blade manufacturingtechniques well-known in the art.

[0017] As best seen in FIG. 3, human cornea 200 has several layers. Theoutermost layer is epithelium 210, followed by Basement Membrane 220,Bowman's Membrane 230, substantia propria or stroma 240, Descemet'sMembrane 250 and endothelium 260. The method of the present inventioninvolves the use of microkeratome 34 having blade 38 to removeepithelium 210 and Basement Membrane 220 while leaving Bowman's Membrane230 relatively intact. The method of the present invention usesmicrokeratome 34 in a conventional manner well known to those skilled inthe art. The oscillation frequency of blade 38 preferably isapproximately between 5,000 revolutions/minute and 20,000revolutions/minute, with approximately between 8,000 revolutions/minuteand 14,000 revolutions/minute being most preferred. The speed of blade38 as it traverses cornea 200 preferably is approximately between 1.0millimeter/second and 2.0 millimeters/second, with approximately 1.5millimeters/second being most preferred. As blade 38 approaches cornea200, blunt tip 114 penetrates epithelium 210 and Basement Membrane 220,but is insufficiently sharp to penetrate Bowman's Membrane 230. As aresult, blunt tip 114 and rounded portion 112 scrape along the surfaceof Bowman's Membrane 230, separating epithelium 210 and BasementMembrane 220 from Bowman's Membrane 230 without damaging Bowman'sMembrane 230. Following such separation, Bowman's Membrane 230 andstroma 240 are irradiated as in a conventional laser refractive surgicalprocedure, see for example, U.S. Pat. Nos. 4,784,135 (Blum, et al.) and4,903,695 C1 (Warner, et al.), the entire contents of which beingincorporated herein by reference.

[0018] This description is given for purposes of illustration andexplanation. It will be apparent to those skilled in the relevant artthat changes and modifications may be made to the invention describedabove without departing from its scope or spirit.

We claim:
 1. A microkeratome blade, comprising: a) a flat side; b) atapered side having a rounded portion; and c) a blunt tip connecting theflat side to the tapered side at the rounded section, the blunt tipbeing sized and shaped so that the blade penetrates an epithelium and aBasement Membrane of the cornea so as to expose but not penetrate aBowman's Membrane of the cornea when the blade is advanced over thecornea.
 2. The microkeratome blade of claim 1 wherein the roundedportion has a radius of between about 0.025 millimeters and 0.200millimeters.
 3. The microkeratome blade of claim 1 wherein the blunt tiphas a length of between approximately 0.001 millimeters and 0.050millimeters.
 4. The microkeratome blade of claim 3 wherein the blunt tiphas a length of between approximately 0.005 millimeters and 0.025millimeters.
 5. The microkeratome blade of claim 1 wherein the blunt tipis ground at an offset angle relative to the rounded portion at betweenapproximately between 0 degrees and
 60. 6. The microkeratome blade ofclaim 5 wherein the blunt tip is ground at an offset angle relative torounded portion of approximately between 0 degrees and 20 degrees.